NEUROANATOMICAL DISTRIBUTION OF AROMATASE MESSENGER-RNA IN THE RAT-BRAIN - INDICATIONS OF REGIONAL REGULATION

Aromatase, the enzyme responsible for the conversion of testosterone t o estradiol, is found in the rat brain and is present in regions of th e preoptic area, hypothalamus, and limbic system. Gonadal steroid horm ones regulate aromatase activity levels in many brain regions, but not all. Using in situ hybridization, we examined the distribution of aro matase mRNA in the adult male forebrain, as well as the levels of arom atase mRNA in the brains of males and females, and the regulation by g onadal steroid hormones. In the adult male, many heavily labelled cell s were found in the encapsulated bed nucleus of the stria terminalis ( BNST), the medial preoptic nucleus (MPN), the ventromedial nucleus (VM N), the medial amygdala (mAMY) and the cortical amygdala (CoAMY). The regional distribution of aromatase mRNA was similar in males and femal es, but males tended to have a greater number of aromatase mRNA-expres sing cells in each region compared to females. Aromatase mRNA levels i n the BNST, MPN, VMN and mAMY tended to be lower in castrated males th an in intact males, whereas aromatase mRNA levels were unaltered by ca stration in the CoAMY. Further analysis of individual cells expressing aromatase mRNA suggests that aromatase mRNA may be regulated by stero id hormones differentially in specific populations of cells in regions where enzyme activity levels are steroid-hormone-dependent. (C) 1997 Elsevier Science Ltd.